In blow molding apparatus,, the coating applied to the core rods is generally applied by injection molding and the material is at very high temperature as it comes from the injection mold. In order to obtain biaxial orientation of the plastic during the blowing operation, the plastic must be cooled to a temperature approaching its hardening or crystallizing temperature. If the apparatus is operated slowly enough to permit the parison to cool to orientation temperature while travelling from an injection mold to a blowing mold, the production rate of the apparatus is greatly impaired.
This invention obtains the necessary time for controlling the temperature of the parison without reducing the speed of the machine cycle. This result is accomplished by having each core rod, after being coated with a parison, move into an inactive position before reaching the blowing station. The core rod remains in this inactive position, where it does not interact with any stations of the machine, and passes through a full cycle of travel and back past the station at which it was coated and to the location at which it moved into inactive position.
Each successive core rod is then returned to its active position and passes on to the blowing station and stripper station in accordance with conventional operation.
During this extra cycle of movement of each core rod, its temperature can be controlled so that the parison will be at orientation temperature when it reaches a blowing station. The time can also be used to reduce the temperature of the parison to a low enough temperature so that another coating of plastic can be applied over the cooled parison without impairing the cooled parison, if it is desired to make a molded article of laminated construction.
Where the apparatus is constructed for biaxial orientation of the blown article, the blowing is preferably carried out in two stages. The parison is first introduced into a blowing mold which is shaped so that the blowing in this first blowing mold expands the parison to a much greater degree in a direction lengthwise of the core rod for orientation in that direction. The partially blown article is then carried to a second blowing mold where the cavity is of larger diameter so that the blowing operation in the second blowing mold increases the diameter of the blown article and thus provides orientation in a circumferential direction.
Where a laminated product is to be blown, a second injection mold is substituted for the first blowing mold and the core rod with two layers of plastic on it is then moved to a blowing station where both layers are blown simultaneously to produce a laminated container or other article.
In order to obtain more control of the change in temperature of the parison while moving through the cycle for temperature control, a chamber is provided with an open side into which the core rods that are in inactive position can travel while subject to contact with fluid used to control the temperature of the parison. Usually this fluid will be at a substantially lower temperature than the plastic of the parison since the temperature control required for orientation or for the extrusion of a subsequent layer of plastic, is a reduction in temperature. The temperature control fluid, usually air, is circulated by control means that are adjustable to regulate the temperature of the temperature control fluid.
In the preferred embodiment of the invention, the core rods extend outwardly from an indexing table when in active position for cooperation with the coating station, blowing station and stripper station. The core rods are moved into inactive positions by swinging them upwardly or downeardly into positions where they extend in directions having substantial components that are parallel to the axis of rotation of the indexing table. Temperature controlling chambers are provided both above and below the indexing table so as to receive the core rods that extend downwardly as well as those which extend upwardly. The chamber has a wider portion at a location between the coating station and the first blowing station so that there is space for core rods to swing between active and inactive positions at this wider space between the coating and blowing stations.